Fluid-dynamic engine

ABSTRACT

This invention relates to a fluid-dynamic engine wherein a gas is accelerated through the engine at the speed of sound at the sonic speed of the gas and imparting energy to the gas while maintaining it at the sonic speed. The engine may comprise a duct having a sonic duct section interposed between convergent and divergent sections so that it is successively accelerated to the sonic speed through the convergent section at the sonic speed. The engine includes means for deriving power from the fluid stream by coupling a fluid-responsive element to the stream and recompressing the fluid of the fluid stream while moving at the sonic speed.

United States Patent [72] Inventor Giusto Fonda-Bonardi Los Angeles,Calif.

[2]] Appl. No. 817,490

[22] Filed Apr. 18, 1969 [54] FLUID-DYNAMIC ENGINE 9 Claims, 4 DrawingFigs.

[52] 11.8. CH 60/59, 60/39.02, 60/264 [51] llnt.Cl F0lk3/l8, F02c 9/00,F02k 1/00 [50] Field of Search ..60/59, 59 T,

Primary Examiner- Edgar W. Geoghegan Attorney-Christie, Parker & HaleABSTRACT: This invention relates to a fluid-dynamic engine wherein a gasis accelerated through the engine at the speed of sound at the sonicspeed of the gas and imparting energy to the gas while maintaining it atthe sonic speed. The engine may comprise a duct having a sonic ductsection interposed between convergent and divergent sections so that itis successively accelerated to the sonic speed through the convergentsection at the sonic speed. The engine includes means for deriving powerfrom the fluid stream by coupling a fluidresponsive element to thestream and recompressing the fluid ofthe fluid stream while moving atthe sonic speed.

llllll -llllll 1 I l a 1 PATENTED AUBITIQYI 3,599,431

[l ll ll l lg lllll llllll ll A A 611/5 70 F'OAAOA-EOA/A RD/FLUID-DYNAMIC ENGINE This application is an improvement over theteachings of my earlier filed copending application bearing Ser. No.798,367 and entitled FLUID-DYNAMIC ENGINE." Briefly, the device thereindescribed is characterized by the process of heating a gas which ismoving at the speed of sound in a duct of suitable shape, and by theutilization of the resulting increase of kinetic energy of the gas. Theshape ofthe duct is related to the rate of heat delivery to the gas, soas to maintain the velocity of the gas equal to the local speed of soundover substantially the entire length of duct wherein the heat deliveryprocess takes place. Conversely, this means that, once a duct is builtwith a certain profile of cross sections matched to a given profile ofheat delivery rate, the heat delivery rate cannot be changed much fromthe design profile without causing the flow to deviate from the desiredcondition of sonic velocity. As a consequence an engine of this type canbe designed to operate very efficiently for a fixed value of rate ofheat absorption and power output, but does not lend itself easily tochanges of power output.

There are two kinds of variation of power output that are of greatpractical interest. One is the adjustment of operating conditions to anoptimum set of values resulting in the most efficient operation forrelatively long periods of time: an example of this is the adjustment ofoperating conditions of an airplane engine for most efficient cruise ata given altitude with a given gross airplane weight. The other is thequick variation of power setting required for maneuvers, e.g., takeoffsand landings. Here responsiveness is more important than optimumutilization of thermal energy in the engine. Similarly, a ship requiresresponsive variations of propeller power for docking maneuversindependently from the need for efficient propulsion during cruise.These two distinct requirements can be separately met by two differentcontrivances, which can, however, be both simultaneously applied to thesame engine. Accordingly, this invention refers to means for quickly andresponsively varying the power output of a fluid-dynamic engine of thetype described in the aforementioned copending application, in the casein which the power output is extracted from the engine in the form ofmechanical power delivered to a rotating shaft.

These and other features of the invention can be more fully appreciatedthrough reference to the drawings forming part of this specificationwherein:

FIG. I is a diagrammatic cross-sectional view of a fluiddynamic engineembodying the present invention;

FIG. 2 is an end view of the engine of FIG. 1 taken along the lines 2-2and 2-A, and

FIGS. 3 and 4 show two positions of the power output devicecorresponding respectively to maximum power output and zero poweroutput.

The structure and operation of the basic fluid-dynamic engine isdescribed in the aforementioned copending patent application and thedisclosure thereof is incorporated herein by reference and a moredetailed appreciation of the operation of the type of fluid-dynamicengine under consideration may be had by reference to said copendingapplication. Briefly, for the purposes of the present invention, thefluid-dynamic engine E comprises a duct D for conveying a fluid streamthereto. The duct D has a convergent section 10 where the fluid or gasis accelerated to Mach 1 by an adiabatic expansion. The gas then entersthe sonic section 111 of the duct D wherein heat is delivered to thefluid while it is moving at sonic speed. The fluid travelling at sonicspeed then enters the diffuser section 15. At this point the gas has apressure P equal to the critical pressure, conventionally indicated byP*, related to the stagnation pressure P, by

P#=[ )lk/(A'IUPD where k is the ratio of specific heats in the gas. Thisis a general relationship and applies for all gases moving at the speedof sound. For air, i=1 .40 and P*=0.528 P The moving gas containskinetic energy, of which a part is used to compress the gas in asubsonic diffuser to a pressure closer to P and a part remains availablefor utilization. It is therefore important that recompression beeffected with a minimum of losses, in particular frictional losses,Since frictional losses occur predominantly in the boundary layer, wherethe moving gas is in contact with a solid wall, and are proportional tothe velocity of the gas (which varies in a prescribed manner between twofixed predetermined limits, i.e., between the speed of sound at the exitof the sonic section and a preselected lower velocity at the end of thediffuser), the total frictional loss is essentially proportional to whatis called the wetted area, or the wall area of the duct in contact withthe boundary layer. This, for a given diameter, is in turn proportionalto the length of the diffuser. It is therefore important to build theshortest diffuser possible compatible with the requirement of effectiverecompression.

On the other hand, the adverse pressure gradient present in the diffusertends to increase the thickness of the boundary layer as the gasprogresses along the diffuser. If the pressure gradient is too steep theboundary layer becomes detached, the diffuser stalls, and norecompression is possible beyond the point of detachment. Henceeffective diffusers cannot be built shorter than a minimum lengthimposed by the requirement that the pressure gradient be less steep thanthat which causes boundary layer detachment. Within these limitations,the most effective diffuser is the one which has the least wall area inproportion to the cross-sectional area of the duct.

An optimal diffuser, in this sense, can be built by taking advantage ofthe fluid-dynamic properties of a free jet impinging on a perpendicularflat plate. A free fluid stream, issuing at high velocity from anorifice (assumed of circular shape) and impinging on a flat plateperpendicular to the axis of the stream, is deflected radially away fromthe center of impingement, which is a point of stagnation. At this pointthe fluid is momentarily at rest and full stagnation pressure P, isdeveloped without any frictional losses, because the moving gas arrivingthere is nowhere in contact with any walls. The stagnation point issurrounded by a region in which most of the original kinetic energy ofthe gas arriving there is converted in pressure, whereby the gas comesarbitrarily close to stagnation, again without being in contact with anywalls. This region is in turn surrounded by another in which thepressure is lower and more unconverted kinetic energy remains availableand so on. The stream can be ideally subdivided in concentric streamtubes, separated by ideal stream surfaces, which are concentric surfacesof revolution each generated by a typical streamline rotated about theaxis of symmetry. Each concentric stream tube is characterized by amaximum value of recovered pressure, which occurs at the point where thestreamline in question is tangent to a surface of equal pressure in thefluid. Each streamline (and each corresponding stream tube) can belabeled with a characteristic value of the pressure ratio P,.lP where Pis the maximum value of pressure recovered, and P, is the stagnationpressure (which is fully recovered at the center of the plate). If thewall of the diffuser is shaped to coincide with that stream surfacewhich corresponds to some desired value of P lP and extended to thepoint where said pressure ratio is developed in the fluid in contactwith the wall (i.e. to the line where said wall is tangent to thesurface of equal pressure km), then the flow inside is unaffected by thewall and the same pressure ratio P /P appears at all points of thesurface of equal pressure, imbedded in the fluid, for which P=P Thissurface intersects said plate along a circular line concentric to thestagnation point: the plate must extend at least to this line.

Under the simplifying assumption that the gas density does not depend onpressure (which is valid in the neighborhood of the stagnation point),the properties of the flow are best described in terms of the velocitypotential (see, for example, L, Prandtl and O. G. Tietjens, Fundamentalsof hydroand aeromechanics, Dover, N.Y. i957, p. l43). It is easily foundthat the flow is axially symmetrical and that all streamlines in eachplane passing through the axis are cubic hyperbolas described by theequation R Z=C (l) where R is the radius, Z is the distance from saidplate, and, C

an arbitrary constant related to the pressure ratio P /P One suchstreamline is shown as arrow 101 in FIG. 1. All streamlines aregeometrically similar and any one of them can be used to generate asurface of revolution which, together with a plate 102, defines apossible and acceptable geometry for the diffuser. The coordinates forthe diffuser wall 103 are computed by choosing an appropriate value forthe arbitrary constant C in equation 1. Within this envelope the gasrecompresses to full stagnation pressure P, at the central point 104 ofplate 102. The surfaces of equal pressure are portions of oblatedellipsoids, each intersecting the plane of the paper of FIG. 1 along aellipse, for example as represented by the dotted lines 105 and 106,each identified by a particular value of the pressure ratio P /P Theline 106 is tangent to the diffuser wall 102 at point 107 and definesthe exhaust compression ratio P /P, for which the diffuser is designedWall 103 is extended to point 107 and needs go no further to providerecompression to a pressure ratio equal to P /P Point 107 as shown inFIG. 1 is, of course, the intersection with the plane of the paper of acircular boundary concentric with the axis of the machine.

The above-described profile is rigorously correct only if the fluiddensity is constant. This is very nearly true at the end of therecompression process, but not so where the gas pressure P is stillclose to the critical pressure P*, for which M=l. There is, in fact, asubstantial variation of density associated with the very large pressureratio P,./P* for which the diffuser must be designed. This effect,called compressibility effect, is negligible in the neighborhood ofplate 102, but is predominant in the region immediately downstream ofsonic section 11, where M=l and #Pi Although it is possible to developdifferential equations which describe the stagnation of a compressiblefree jet against a perpendicular flat plate, their solution is difficultand can be best handled by a digital computer. The result is a profilequite similar to that described by equation 1, but generally somewhatwider and less tapered near the exit of sonic section 11. A very goodapproximation of this rigorous profile can be obtained by noting thatcompressibility effects are negligible by the time the fluid is sloweddown to a Mach number smaller than about 0.3. The diffuser can bedivided in two parts, of which part 108 is designed on the basis of aconstant pressure-ratio gradient, and part 109 which is designed inaccordance with equation I. The two parts are joined at a point 111where the Mach number M is approximately equal to 0.3, and the ductprofile is computed by imposing the condition that all flow propertiesand their derivatives be continuous across this point. A smallcorrection is then applied to the profile (whether rigorously generatedby digital computer, or approximated as described above), to allow forthe growth of the boundary layer: the correction consists of adisplacement of the wall outwards by an amount equivalent to theboundary layer thickness at each point of the diffuser.

A diffuser designed in accordance with this disclosure has two importantproperties which are needed in the implementation of this invention:

a. It can recompress a gas from a pressure ratio P/P equal to thecritical pressure ratio P*/P,, (where M=l to an exhaust pressure ratioP,,/P,, arbitrarily close to unity (for which the Mach number would beequal to zero), without suffering boundary layer separation and withvery low frictional losses of kinetic energy.

b. It deflects the momentum vector associated with the moving fluid froman axial direction (at the end of sonic section 11, where the fluid ismoving in an essentially parallel stream) to a symmetrically radialdirection at the exhaust of the diffuser between plate 102 and theboundary 107 of the sidewall 103, as indicated by the tip of thestreamline arrow 101. The turning of the momentum vector is causes bythe radial component of the pressure gradient between equal pressuresurfaces (eg 105 and 106), and does not require any turning vanes in thestream, with associated frictional and turbulent losses of kineticenergy. It should be noted, parenthetically, that the diffuser heredescribed can be used in applications other than fluid-dynamic engines,of the type under consideration, whenever a fluid must be recompressedby converting part of its initial kinetic energy over a large pressureratio: ifthe fluid is incompressible (e.g. a liquid), equation 1 may beused without compressibility corrections.

The radially moving gas at the exhaust of the diffuser isimparted'angular momentum by a ring of curved vanes mounted betweenplate 102 and a flangelike extension 112 of the diffuser wall 103. Thecurved vanes 120' are designed to have a radial extension such that theydo not protrude beyond an elliptical contour coincident with theconstant-pressure ellipsoid 106, which defines the exhaust of thediffuser proper, and is also a surface of constant gas velocity; andsuch that they terminate on a straight cylindrical surface 113 on theoutside. The curvature of the vanes is computed to provide channels ofconstant area 121 between them, so as to turn the momentum vector of thegas without changing its magnitude, and to eject the gas at a constantangle a with the tangent plane 126 to the cylindrical surface 113 atevery point of the surface. The gas impinges then on a ring of turbineblades 122 designed to utilize the angular momentum of the gas andhaving the customary inlet and outlet angles appropriate to the velocityof the gas and the tangential angle a. Since the gas emerges uniformlyfrom surface 113 and has everywhere the same velocity and the sametangential angle a, the turbine blades 122 have a constant profile andno twist, and can be cheaply fabricated from simple extruded bars ofappropriate cross section. The blades are oriented parallel to the axisof the machine and parallel to the cylindrical surface 113, They aremounted between a support ring 114 and a wheel 115, carried by a hub116.

The torque collected by the turbine is transmitted to the output shaft117 by means of a spline comprising an outer element 123 attached towheel 115 and an inner element 124 attached to shaft 117. The splinepermits the entire wheel, hub and blades assembly to move axially whilenormally rotating and transmitting torque to shaft 117. The axialposition of the turbine assembly is controlled, for example, by acontrol lever 118 engaged in a groove 119 cut around hub 1 16.

The extent of the axial movement of wheel 115 is sufficient to place theturbine blades 122 across the entire width of the exhaust of thediffuser (surface 113), or to retract them entirely clear of theemerging stream of gas. FIG. 1 shows the turbine in'an intermediateposition. FIG. 3 shows the blades fully engaged, and intercepting theentire efflux from the diffuser. FIG. 4 shows the blades fullyretracted, and not touched by the emerging gas stream 125. It is clearthat the device can pass from developing full torque to zero, and viceversa, simply by translating axially wheel 115 from one extreme to theother of the travel on spline 123-124 and back. Intermediate values ofthe torque can be selected by stopping the axial translation in anintermediate position.

When the wheel is in an intermediate position, as shown in FIG. 1 itextracts from the gas stream only the kinetic energy of that fraction ofthe entire gas stream which engages blades 122. The remainder, passingbetween flange 112 and ring 114, is not utilized: the kinetic energy iseventually dissipated in turbulence and is lost to the machine. For thisreason the device here described is best used when the loss of somekinetic energy is of scarce importance compared with the need for quickchanges of power output/Since the power delivered by a rotating shaft isequal to the product of the torque times the angular speed, and thetorque developed is proportional to the fraction of exhaust stream 125engaged by blades 122, the power output can be changed without changingthe angular speed of the shaft, which is an advantage in certainapplications. This can be done by varying the torque, simply bytranslating the wheel axially on spline 123-124. This is contrasted withthe slow change of power output which can be obtained from otherturbines in which the angular momentum of the entire spinning assembly,sometimes very large, must be changed to change the output power.

When quick changes of power output are not desired, a loss of kineticenergy is avoided by leaving blades 122 fully engaged with the exhaustgas stream as shown in FIG. 3. This is the normal operating position forthe device when the desired power output is expected to remain constantor to change but slowly, and time is available for adjusting the powerlevel of the device by other means.

What I claim is:

l. A fluid-dynamic engine for the transformation of heat energy intomechanical energy comprising a fluid-conveying duct having a sonic ductsection interposed between a convergent section and a divergent section,

means for conveying fluid through each section of said duct so that itmoves in a fluid stream at the speed of sound in said fluid through thesonic section,

means for heating the fluid stream while it is moving at said sonicspeed,

drive means including a rotatable shaft coupled to the downstream sideof the divergent section for deriving power from the fluid dynamicengine in the form of rotations of the shaft,

said fluid stream impinging on said drive means for imparting the energyof the fluid stream to said drive means,

and means for controlling the coupling between said fluid stream andsaid drive means for controlling the power extracted from the engine andthereby the rotations of the shaft.

2. A fluid-dynamic engine as definedin claim 1 wherein the divergentduct section is constructed and defined for recompressing the fluidstream and redirecting the fluid stream into a path for impingement ontosaid drive means. V

3. A fluid-dynamic engine as defined in claim 2 wherein the divergentduct section includes a solid terminal portion upon which the fluidstream impinges and recompresses a portion of the fluid stream tostagnation pressure and includes a ring of curved vanes for redirectingthe fluid stream.

4. A fluid-dynamic engine as defined in claim 3 wherein the drive meanscarries turbine blades adapted for receiving the fluid stream emergingfrom the curved vanes when coupled thereto.

5. A fluid-dynamic engine as defined in claim 4 including means forcontrolling the coupling of the drive means to vary the extent ofimpingement of the fluid stream with the turbine blades and thereby thepower derived from the engine.

6. A method of operating a fluid-dynamic engine including the steps ofaccelerating a fluid stream through an engine at the speed of sound atthe sonic speed of the fluid,

imparting energy to the fluid while maintaining it at said sonic speed,

recompressing the fluid stream to stagnation pressure, and

deriving torque from the energy of the fluid stream.

7. A method for deriving energy from a fluid-dynamic engine includingthe steps of accelerating a fluid stream through an engine at the speedof sound at sonic speed in the fluid,

imparting energy to the fluid stream while it is moving at said sonicspeed,

passing the fluid through a diffuser at subsonic speeds for maintainingthe fluid moving at sonic speed while energy is being imparted to it,

coupling a fluid-responsive element to the stream for deriving powertherefrom, and

recompressing the fluid of the fluid stream passing through the diffuserand deriving power from the fluid stream.

8. A method as defined in claim 7 including the step of redirecting thepath of the fluid stream in the diffuser prior to coupling to thefluid-responsive element.

9. A method as defined in claim 7 wherein said diffuser is representedby a solid surface shaped to coincide with the shape ofa selectedstreamline surface such as would naturally result in the impingement ofan otherwise unrestricted fluid stream of the same characteristicsstagnating against said solid terminal portion.

1. A fluid-dynamic engine for the transformation of heat energy intomechanical energy comprising a fluid-conveying duct having a sonic ductsection interposed between a convergent section and a divergent section,means for conveying fluid through each section of said duct so that itmoves in a fluid stream at the speed of sound in said fluid through thesonic section, means for heating the fluid stream while it is moving atsaid sonic speed, drive means including a rotatable shaft coupled to thedownstream side of the divergent section for deriving power from thefluid-dynamic engine in the form of rotations of the shaft, said fluidstream impinging on said drive means for imparting the energy of thefluid stream to said drive means, and means for controlling the couplingbetween said fluid stream and said drive means for controlling the powerextracted from the engine and thereby the rotations of the shaft.
 2. Afluid-dynamic engine as defined in claim 1 wherein the divergent ductsection is constructed and defined for recompressing the fluid streamand redirecting the fluid stream into a path for impingement onto saiddrive means.
 3. A fluid-dynamic engine as defined in claim 2 wherein thedivergent duct section includes a solid terminal portion upon which thefluid stream impinges and recompresses a portion of the fluid stream tostagnation pressure and includes a ring of curved vanes for redirectingthe fluid stream.
 4. A fluid-dynamic engine as defined in claim 3wherein the drive means carries turbine blades adapted for receiving thefluid stream emerging from the curved vanes when coupled thereto.
 5. Afluid-dynamic engine as defined in claim 4 including means forcontrolling the coupling of the drive means to vary the extent ofimpingement of the fluid stream with the turbine blades and thereby thepower derived from the engine.
 6. A method of operating a fluid-dynamicengine including the steps of accelerating a fluid stream through anengine at the speed of sound at the sonic speed of the fluid, impartingenergy to the fluid while maintaining it at said sonic speed,recompressing the fluid stream to stagnation pressure, and derivingtorque from the energy of the fluid stream.
 7. A method for derivingenergy from a fluid-dynamic engine including the steps of accelerating afluid stream through an engine at the speed of sound at sonic speed inthe fluid, imparting energy to the fluid stream while it is moving atsaid sonic speed, passing the fluid through a diffuser at subsonicspeeds for maintaining the fluid moving at sonic speed while energy isbeing imparted to it, coupling a fluid-responsive element to the streamfor deriving power therefrom, and recompressing the fluid of the fluidstream passing through the diffuser and deriving power from the fluidstream.
 8. A method as defined in claim 7 including the step ofredirecting the path of the fluid stream in the diffuser prior tocoupling to the fluid-responsive element.
 9. A method as defined inclaim 7 wherein said diffuser is represented by a solid surface shapedto coincide with the shape of a selected streamline surface such aswould naturally result in the impingement of an otherwise unrestrictedfluid stream of the same characteristics stagnating against said solidterminal portion.